THERMAL RUNAWAY
Marlin 3D Printer Firmware
Severity: CriticalWhat Does This Error Mean?
Thermal Runaway in Marlin firmware means the temperature deviated from what is expected — either the heater is out of control or the temperature reading is unreliable. This is a fire safety feature. The printer halts to prevent danger. Check thermistor, heater, PID tuning, and drafts.
Affected Models
- All Marlin-based 3D printers
Common Causes
- Thermistor loose or disconnected — temperature reading jumps
- Heater cartridge loose — inconsistent heating
- Draft or fan cooling the hotend unexpectedly
- PID values incorrect for the hardware
- Firmware thermal protection thresholds too tight
How to Fix It
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Check the thermistor is properly seated in the heater block.
The thermistor must be firmly held in place by its retaining screw. A loose thermistor gives erratic readings that trigger thermal runaway.
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Tighten the heater cartridge in the heater block.
A loose heater moves in its hole, causing temperature fluctuations.
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Run PID autotune.
M303 E0 S200 C8 then M500 to save. This teaches the firmware how to maintain stable temperature with your hardware.
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Eliminate drafts around the printer.
A draft can cool the hotend suddenly, making the firmware think something is wrong. Use an enclosure or move the printer away from windows and AC vents.
Frequently Asked Questions
Should I increase the thermal runaway thresholds?
Only slightly, and only if PID tuning and hardware checks do not fix the issue. Making thresholds too wide defeats the purpose of the safety feature.
Which 3D printers use Marlin firmware?
Most consumer FDM printers run Marlin or a derivative: Creality Ender/CR series, Anycubic Kobra, Artillery, Tronxy, and many others. Prusa uses their own fork of Marlin. Bambu Lab uses their own firmware.